Abstract: A method for simultaneously detecting and separating a target analyte such as a protein or other macromolecule that includes providing a porous silicon matrix on the silicon substrate, exposing the porous silicon matrix to an environment suspect of containing the target analyte, observing optical reflectivity of the porous silicon matrix; and correlating the changes in the silicon substrate to the target analyte.

Abstract: An optical element for resonating and reflecting incident light having a wavelength includes a periodic structure formed of protrusions and recessions. A period of the periodic structure is equal to or less than the wavelength of the incident light. The incident light having the wavelength is resonated and reflected by a resonance caused between the incident light and the protrusions and recessions. Widths of the protrusions are spatially changed.

Abstract: A near-IR laser laser-and-corner cube system for determining the refractive-index structure parameter by providing the return power of the retroreflected laser beam from the corner cube, which return power correlates to the refractive-index structure parameter. The system is economical, physically containing only (1) the laser which emits a near-IR wavelength output beam, (2) a 50/50 splitter, to receive back the retroreflected return beam from the corner cube along the same optical axis as the output beam, in a monostatic configuration; (3) the target corner cube; (4) a receiving focus lens; (5) a spectral filter and (6) a power meter to provide the monostatic measurement of the return power. Critically the ratio of the area of the corner cube to that of the receiving focus lens is at least 1:2, to obtain meaningful power measurements—to correlate to pre-calculated refractive-index structure parameters.

Abstract: A method of controlling a light beam in an optical system includes a light source that directs a collimated light beam along a path, through a sample, and toward the active area of a stationary detector. The method includes the step selectively moving a lens into the path of the light beam for spreading the beam in instances where the path of the beam is altered by the sample between the source and the stationary detector The detector, therefore, is held stationary. Adjustment means are provided for increasing the intensity characteristic of the light that reaches the detector to account for a decrease in intensity that occurs when the lens is in the path of the light beam to spread the beam.

Abstract: A measurement device for the determination of the characteristics of the object's surface by means of the optical radiation, wherein a measurement device comprises an optical radiation source and a detector to receive the radiation reflected from the surface being measured. In addition, a measurement device comprises an emitted optical radiation processing unit, which is adjusted to split optical radiation emitted by an optical source into separate wavelengths and to direct said separate wavelengths to the object being measured in a direction, that differs from the normal of the surface being measured so, that at least the shortest and the longest wavelengths of said wavelengths are focused on different halves and different heights of the measured object's surface, in the direction of the normal of the surface being measured.

Abstract: Described herein are devices and methods for making extremely accurate measurements in a medium by continuously measuring the index of refraction of the medium such as water or biological tissue. Also described herein is a device for constantly measuring the index of refraction, and using the index of refraction data to constantly calibrate the optical measurement device. In addition, a primary measurement device (a ladar) that is optimized for data collection in a volume backscattering medium such as water or biological tissue is described, along with data results from the lab.

Abstract: A portable liquid design system includes a portable information handling system (IHS) that employs a liquid design application capable of operating in different modes to design different liquids such as corn syrup, espresso, coffee, soda pop and others. The portable liquid design system may include a refractometer to measure the refractive index and temperature of a liquid under test. The liquid design application may apply the measured refractive index and temperature to a 3 dimensional representation of the correlation of refractive index, temperature and concentration (% total dissolved solids) to determine a particular concentration corresponding to the measured refractive index and temperature. A single 3 dimensional scale may apply to virtually all values of interest of refractive index, temperature and concentration for a particular liquid under test.

Abstract: A semiconductor laser based intra-cavity optical micro-fluidic biosensor comprises a coupled-cavity semiconductor laser, a 2×2 coupler and a phase adjustment section on one input port of the coupler. The dominant mode of the coupled-cavity laser appears in one output port of the coupler, while the adjacent mode comes out from the other output port of the coupler. The resonant frequency interval of the sensing cavity is slightly larger or smaller than one half of that of the reference cavity. Part of the sensing cavity is the sensing section which is covered by an analyte. The refractive index change of the analyte will cause the lasing mode of the coupled cavity to switch to an adjacent mode, resulting in a ?-phase change in the phase difference between the two output ports of the two resonance cavities. By applying the Vernier effect, the power ratio of the two output ports of the coupler will change and the refractive index change of the analyte can be derived.

Abstract: According to embodiments of the present invention, an optical sensing system is provided. The optical sensing system includes a resonator arrangement including a first resonator, wherein an effective refractive index of the first resonator is changeable in response to a change in a refractive index of a cladding of the first resonator, and a second resonator to which a current or voltage being adjustable in response to a change in the effective refractive index of the first resonator is applied, wherein the optical sensing system is configured to determine the change in the effective refractive index of the first resonator based on a change in the current or voltage applied to the second resonator. Further embodiments provide a method of determining a change in an effective refractive index of a resonator of an optical sensing system.

Abstract: The present invention relates to a thermally compensated optical sensing system for identifying various types of liquid fuels and/or the ratio in liquid fuel mixtures on real time. In this system, an optical fiber is used as a light guide and a sensor device for determining the refractive index of liquid fuels through the principle of reflectivity. Starting from a light source, light is transmitted interiorly of the optical fiber to the test probe which is in contact with the fuel. The optical signal resulting from the interaction between light and fuel is a function of refractive indexes of the optical fiber and the fuel, the wavelength of light used, and the fuel temperature. The system proposed herein relates to the use of this optical system in liquid fuels by using optical fibers having suitable refractive indexes as a function of the fuel type and/or fuel mixture being analyzed, allowing the sensitivity of the optical system to be optimized according to application requirements.

Abstract: Optical systems and methods are described that provide greater solving power for thin-film measurements in general, and provide a unique model-free solution for single-layer films in particular.

Abstract: Refractive index tools and method. A refractive index tool includes a wave source configured to generate a wave; a transparent rod configured to receive the wave from the wave source; and a wave detector configured to receive the wave from the transparent rod. The wave source is provided at a first end of the transparent rod and the wave detector is provided at the first end or a second end of the transparent rod so that the wave emitted by the wave source travels through the transparent rod and experiences total internal refraction prior to arriving at the wave detector.

Abstract: A tunable metamaterial structure, comprises a flexible substrate capable of being strained, a metamaterial pattern on a surface of the flexible substrate, and a metal layer on the metamaterial pattern. The flexible substrate of the tunable metamaterial structure is a strained and relaxed substrate which has been strained to a degree sufficient to register a resonant response upon relaxation that is shifted relative to the resonant response of the flexible substrate prior to being strained. The application of strain to the flexible substrate of the metamaterial structure enables tuning of the resonant frequency.

Abstract: The method measures first transmitted wavefronts and second transmitted wavefronts by respectively causing reference light to enter an object placed in plural placement states in a first medium and a second medium, calculates an aberration sensitivity with respect to changes of the placement state of the object, and calculates an alignment error of the object in each placement state by using the aberration sensitivity and the first and second transmitted wavefronts measured in each placement state. The method further calculates first and second reference transmitted wavefronts respectively acquirable when causing the reference light to enter the reference object placed in placement states including the alignment errors in the first medium and the second medium, and calculates a refractive index distribution of the object which a shape component thereof is removed, by using the first and second transmitted wavefronts and the first and second reference transmitted wavefronts.

Abstract: Described herein are devices and methods for making extremely accurate measurements in a medium by continuously measuring the index of refraction of the medium such as water or biological tissue. Also described herein is a device for constantly measuring the index of refraction, and using the index of refraction data to constantly calibrate the optical measurement device. In addition, a primary measurement device (a ladar) that is optimized for data collection in a volume backscattering medium such as water or biological tissue is described, along with data results from the lab.

Abstract: A flow-through sensing apparatus includes a flow-head and a sensor that are configured to be selectively coupled through use of a quick-disconnect mechanical coupling. When the sensor is coupled with the flow-head, the sensor cooperates with the flow-head to at least partially define a sensing chamber. The sensor is configured to determine a process parameter, such as refractive index, regarding a substance in the sensing chamber.

Abstract: The present invention is directed to the use of a light absorbing wall material to eliminate stray light paths in light-guiding structures, such as those used for HPLC absorbance detection. More specifically, the present invention relates to the use of carbon-doped Teflon® AF, or “black Teflon® AF,” for all or part of the walls of a light-guiding flowcell adapted for use in HPLC absorbance detection.

Abstract: A downhole fluid analysis tool has a housing and a flow passage for downhole fluid. A device disposed in the tool housing relative to the flow passage has a one or more sources, one or more sensing optics, one or more detectors, and control circuitry. The source generates an input signal. The sensing optic has a refractive index (RI) higher than crude oil and other expected constituents. A sensing surface of the optic optically coupled to the source interfaces with a downhole fluid. When the variable RI of the downhole fluid reaches a defined relationship to the optic's RI, the input signal interacting with the sensing surface experiences total internal reflection, and the reflected signal from the sensing surface remains in the sensing optic and reflects to a detector. The control circuitry monitors the detector's response and indicates gas break out if the response is above a threshold.

Abstract: A refractive index sensor having one or more sources, an adaptive optical element or scanner, imaging optics, a sensing optic, and one or more detectors. The scanner impinges a signal from the source into the sensing optic and onto a sensor-sample interface at sequential angles of incidence. The detector response increases dramatically to signals reflected from the interface at corresponding sequential angles of reflection equal to or greater than a critical angle. The refractive index sensor also uses an input lens between the scanner and the sensing optic and uses an output lens between the sensing optic and the detector. A processor controls the sensor and can determine index of refraction of the fluid sample based on the detector response and scan rate. The sensor can be used in several operational environments from a laboratory to a downhole tool, such as a formation tester to determine properties in a borehole environment.

Abstract: A measuring method includes measuring a sum of an optical path length of a test object and a first medium in a first container, introducing light into an area that includes the first medium but does not include the test object and measuring the optical path length of the first medium, measuring a sum of the optical path length of the test object and a second medium in a second container, the second medium having a refractive index different from that of the first medium, introducing the light into an area that includes the second medium but does not include the test object and of measuring the optical path length of the second medium, and calculating a refractive index of the test object based on the measured optical path lengths and an actual distance of an optical path for which each optical path length is measured.

Abstract: An additive {hacek over (S)}olc filter (ASF) includes i) a first polarizer for receiving an input light, such as from a monochromatic light source, and transmitting a first polarized output, ii) at least one birefringent plate positioned to receive the first polarizer output and transmit an output with wavelength-dependent polarization state, and iii) a second polarizer for receiving the plate output and transmitting a second polarized, filtered output. An ASF spectroscopy system includes the ASF; a monochromatic light source input, e.g. a laser; a sample chamber for exposing a sample to the second polarized, tuned output and generating a signal characteristic of the sample that is filtered by the ASF; and a detector for acquiring the characteristic signal.

Abstract: The present disclosure provides a detecting device of a birefringent lens grating. The detecting device includes a projection pattern disposed adjacent to the birefringent lens grating; an illuminating light source for projecting light onto the projection pattern and the birefringent lens grating; an image capturing device for capturing the light out from the birefringent lens grating and obtaining a projection pattern image of the projection pattern; and a controller for comparing the projection pattern image with a reference to determine a refractive index matching degree of the birefringent lens grating. The present disclosure further provides a detecting method, a manufacture method and a manufacture device of the birefringent lens grating.

Abstract: A measurement method and an evaluating apparatus are provided which are capable of easily and accurately evaluating the light amount of a spot beam, the diffraction efficiency, and the intensity distribution in the optical axis direction by detecting even a weak diffracted beam in an arbitrary wavelength range converged by a diffraction optical element as an imaging lens.

Abstract: A method includes the steps of measuring a first transmitted wavefront in a first medium having a first refractive index and a second transmitted wavefront in a second medium having a second refractive index different from the first refractive index, and obtaining a refractive index distribution projected value of the object in each orientation by removing a shape component of the object utilizing measurement results of the first transmitted wavefront and the second transmitted wavefront and each transmitted wavefront of a reference object that has the same shape as that of the object and a specific refractive index distribution and is located in one of the first medium and the second medium with the same orientation as that of the object, and calculating a three-dimensional refractive index distribution of the object based on a plurality of refractive index distribution projected values corresponding to the plurality of orientations.

Abstract: A microplate for use within an interrogation system and a method of using the microplate are disclosed. The microplate contains within the bottom of each well, an optical waveguide grating based sensor. Approximate to each sensor is a mask having an aperture of predetermined size. The aperture regulates the light that enters and exits the sensor upon successive scans and ensures repeatable readings from the sensor. In an extended embodiment, a method of detection is disclosed that utilizes a launch and receive system while employing the aforementioned microplate.

Abstract: The invention is generally concerned with apparatus and methods for monitoring fluids, in particular critical fluids such as lubricants, in particular oil, based upon evanescent wave techniques. We describe an oil sensor module for use with attenuated total internal (ATIR) reflection apparatus for optically determining the condition of the oil. The sensor module comprises an evanescent wave sensor, preferable in the form of a tapered optical fibre with a high reflectivity mirror at one or both ends; a module housing for said sensor; and an optical connector for connecting said sensor to the ATIR apparatus. Preferably the sensor module is in the form of a dipstick.

Abstract: Method and system for identification of a changed state of a fluid with respect to a reference state of the same fluid, the fluid having an optical parameter changing with the change of the state of the fluid. The method comprises: a) providing an optical arrangement including a transparent enclosure with a portion of the fluid, and an object observable through the optical arrangement, the arrangement being designed such that an image of the object in the changed state of the fluid is optically distinctive from an image of the object in the reference state of the fluid due to change of the optical parameter, at least one of the images being predetermined; b) illuminating the object with diffuse light; c) observing a current image of the object though the optical arrangement along an optical axis; and d) comparing the current image to the predetermined image to identify the changed state of the fluid. The comparison and the identification may be performed by eye or by a sensor with a logical circuit.

Abstract: The invention relates to an optical sensor array detecting a first liquid medium in a second liquid medium by means of the reflection of an emitted light beam of a given wavelength, comprising a light source and an associated receiver, further two circular glass rod lenses running parallel to each other while encapsulated in a housing. The index of refraction of the glass rod lenses is different from those of the liquid media. A reflecting surface is situated opposite the glass rod lenses and is connected to the housing. Said array also comprises a control fitted with a beam splitter, a second receiver and a third receiver, the latter two receivers being configured being mutually opposite.

Abstract: A portable liquid design system includes a portable information handling system (IHS) that employs a liquid design application capable of operating in different modes to design different liquids such as corn syrup, espresso, coffee, soda pop and others. The portable liquid design system may include a refractometer to measure the refractive index and temperature of a liquid under test. The liquid design application may apply the measured refractive index and temperature to a 3 dimensional representation of the correlation of refractive index, temperature and concentration (% total dissolved solids) to determine a particular concentration corresponding to the measured refractive index and temperature. A single 3 dimensional scale may apply to virtually all values of interest of refractive index, temperature and concentration for a particular liquid under test.

Abstract: Novel methods and laser spectroscopic systems for accurately measuring the concentration of compounds are disclosed herein. The disclosed methods utilize a modulation cancellation technique resulting in a significantly increase in the sensitivity and accuracy of laser spectroscopic measurements. In general, the methods and systems utilize modulation phase-shifting and amplitude attenuation to cancel the signals detected from at least two modulated light beams. Thus, any signal detected will be directly proportional to the concentration measurement.

Abstract: An optical indicator (130) for identification of a changed state of a fluid with respect to a reference state of the same fluid, or for monitoring or checking or authenticating a fluid. The fluid has an optical parameter that changes with the change of the state of the fluid. The optical indicator (130) may be attached to or integral with a container or packaging (132) for the fluid. The indicator (130) includes a cavity configured to be filed with the fluid such that the fluid filled cavity forms a variable optical element having an optical performance that varies depending on the changeable fluid's optical parameter. The fluid filled cavity coupled to other optical components of the indicator provides an image that may be compared to a reference image to detect a change of at least one optical property of the fluid as compared to the reference fluid. The comparison may be performed visually or by a suitable detector. The comparison may include automated processing of the detector's output signal(s).

Abstract: The invention relates to a microelectronic sensor device with a light source (21) for emitting an input light beam (L1) into a transparent carrier (11) such that it is totally internally reflected at a contact surface (12) as an output light beam (L2), which is detected by a light detector (31). Frustration of the total internal reflection at the contact surface (12) can then for example be used to determine the amount of target particles (1) present at this surface. The sensor device further comprises a refractive index measurement unit (100, 200, 300) for measuring the refractive index (nB) of the sample medium, and an evaluation unit (50) for evaluating the measurement of the light detector (31) taking the measured refractive index (nB) into account and/or for changing the conditions of total internal reflection of the input light beam (L1).

Abstract: An exemplary refractive-index sensor includes a photonic crystal microcavity structure, a light source, and a detector. The photonic crystal microcavity structure includes a photonic crystal layer having first holes and a second hole defined therein. The first holes are arranged in a regular pattern of staggered parallel rows. The second hole is at an approximate center of the regular pattern, instead of a first hole. A diameter of the second hole is different from that of the first holes. The first holes at each of opposite ends of the row having the second hole are omitted, thereby defining an input waveguide and an output waveguide. The light source is adjacent to the input waveguide. The detector is adjacent to the output waveguide.

Abstract: Plasmonics-active nanostructure substrates—developed on a wafer scale in a reliable and reproducible manner such that these plasmonics-active nanostructures have nano-scale gaps (that include but are not limited to sub-10 nm gaps or sub-5 nm gaps) that provide the highest EM field enhancement between neighboring plasmonics-active metallic or metal-coated nanostructures. The plasmonics-active nanostructure substrates relate to environmental sensing based on SERS, SPR, LSPR, and plasmon enhanced fluorescence based sensing as well as for developing plasmonics enhanced devices such as solar cells, photodetectors, and light sources. Controllable development of sub-2 nm gaps between plasmonics-active nanostructures can also be achieved. Also, the size of the nano-scale gap regions can be tuned actively (e.g., by the application of voltage or current) to develop tunable sub-5 nm gaps between plasmonic nanostructures in a controllable manner.

Abstract: Disclosed is a method and apparatus for determining the birefringence autocorrelation length of a fiber in a non-destructive manner. The PMD of an optical fiber is measured over a first optical spectrum. A Faraday rotation angle is measured over a second optical spectrum. The birefringence autocorrelation length is determined from the measuring of the PMD and the Faraday rotation angle.

Abstract: Methods for detecting the presence and/or volume and/or identity of liquid in a transparent carrier include directing a light source towards the carrier; recording an image of light refracted by the carrier with a camera; and deriving information regarding the presence and/or volume of the liquid in the carrier from the recorded image of the light refracted by the carrier. Devices for detecting the presence and/or volume and/or identity of liquid in a transparent carrier include a camera directed towards the carrier; a light source directed towards the carrier; and means for recording an image of light from the light source as refracted by the carrier and captured by the camera.

Abstract: The method includes first and second steps of placing an object in first and second media whose refractive indices are lower than that of the object, and of causing the reference light to enter the object to measure first and second transmitted wavefronts. When light rays entering a peripheral portion of the object and passing through a same point of the object are defined as first and second light rays, the method causes these light rays to proceed in directions mutually different to change an NA of the reference light such that the reference light after being transmitted through the object is brought closer to collimated light than that before entering the object. The method calculates an effective thickness of the object using geometric thicknesses thereof and calculates a refractive index distribution thereof using the first and second transmitted wavefronts and the effective thickness.

Abstract: A diffraction grating coupler which includes an optical waveguide having a first surface and a second surface opposing the first surface, the optical waveguide having a grating on one of its surfaces. The diffraction grating coupler further includes an elastic polymer film deposited on and attached to the optical waveguide, the elastic polymer film partially surrounding the optical waveguide and leaving one of the two surfaces of the optical waveguide open, the diffraction grating coupler being mountable on a specimen by attaching the elastic polymer film to the specimen.

Abstract: Provided is an apparatus and method for automatically controlling a wiper of a vehicle, the apparatus including a light emitting means to output one or more optical signals to an inside of a front glass of the vehicle, a light receiving means to receive the optical signals output from the light emitting means, and a control means to control the wiper of the vehicle to be driven based on a light receiving efficiency with respect to received signals received by the light receiving means, when operating in an automatic wiper control mode. Since driving of the wiper is automatically controlled based on the light receiving efficiency of optical signals output to the inside of the front glass, it is possible to secure a visual field of a driver without a need to separately manipulate manually a wiper controller.

Abstract: A leak detection sensor for detecting a leakage of an electrolyte solution in a flow battery system is provided. The sensor includes a sensor housing, the sensor housing being at least partially surrounded by a fluid and having mounted therein at least one light source.

Abstract: A substrate characterization device is provided which includes an optical sensor module and a processor. The optical sensor module includes a light emitting source and a light receiving detector for communicating with the substrate and providing an indication of the diffusion of light through the substrate. The indication of the diffusion of light through the substrate is a signal provided to a processor in communication with a memory module for making a comparison of the signal generated by the optical sensor module with a reference signal to determine the quality of the substrate.

Abstract: Certain embodiments of the present invention provide a refractometer including: a housing having an immersion portion, the immersion portion having an opening; a light source for emitting a light; a light sensor for converting a received light into an electrical signal; a prism including faces, including: a first face proximal to the light source and the light sensor; a second face, at least a portion of the second face configured for contacting a sample liquid through the opening, and for forming an interface between the second face and the sample liquid; and a third face, wherein the light travels by: being directed towards the second face; being reflected at least in part by the interface towards the third face; and being reflected at least in part by the third face towards the light sensor. In an embodiment, the refractometer further includes a control portion for receiving the electrical signal, and for determining a refractive index of the sample liquid based at least in part on the electrical signal.

Abstract: Chromatographic separations are often characterized by multiple detectors through which the sample flows serially. As the sample flows between detectors, it becomes progressively diluted due to mixing and diffusion. This phenomenon is traditionally called interdetector “band broadening” and often results in significant distortion of the sample's derived physical properties such as molar mass. This method to characterize the broadening present in a chromatographic system, and an algorithm whereby the narrow peaks of the upstream detector are numerically broadened so they can be compared to the broadened peaks of the downstream detector, is described. Although the technique results in some loss of resolution, its stability and generality allow it a broad range of application. Examples are presented for data collected by dRI, MALS, UV, and viscometric detectors.

Abstract: An inspection instrument includes main unit, Brix testing unit, weight measurement unit, display unit, control unit, and label printer; both of Brix and weight of an object pending test are tested and measured at the same time by the Brix testing unit and the weight measurement unit; resultant data are directly displayed on the inspection instrument by the display unit; data are directly printed on a label; and the label is outputted to be directly attached to the fruit.

Abstract: A method of measuring a porosity of a film, by measuring a refractive index of the film in a first environment having a first relative humidity to produce a first refractive index measurement. The refractive index of the film is measured in a second environment having a second relative humidity, where the first relative humidity is different from the second relative humidity, to produce a second refractive index measurement. Multiple gases can be used to create the first and second environments. The first refractive index measurement and the second refractive index measurement are input into a model that correlates refractive index to film porosity, to output the porosity of the film.

Abstract: An improved refractometer for automatically determining the refractive index of a test subject by using principles embodied in Brewster's Angle, the refractometer comprising a light source, a light detector, a subject mount for securing the test subject to the device, a positioning device to orient the light source and light detector to the subject such that the angles of the light source and light detector to the subject are substantially identical, a data gathering device to automatically retrieve relevant data regarding the angles of the light source and light detector to the subject and the light intensity of the reflected light, and a computational device to process the data using algorithms taking into account the principles embodied in Brewster's Angle and/or Fresnel Equations in order to arrive at the refractive index of the test subject.

Abstract: By using two probe optical systems for measurement by disposing the probe optical systems with a test object sandwiched therebetween, an optical path length of light transmitted through the test object which is identified locally is calculated using an interference signal thereof. In addition, a geometrical thickness of the same part is calculated by measuring positions of the probe optical systems, whereby two calculated values are obtained. Based on the values and a calculated value for a reference object, a refractive index distribution of the test object is obtained.

Abstract: A metrology apparatus is arranged to illuminate a plurality of targets with an off-axis illumination mode. Images of the targets are obtained using only one first order diffracted beam. Where the target is a composite grating, overlay measurements can be obtained from the intensities of the images of the different gratings. Overlay measurements can be corrected for errors caused by variations in the position of the gratings in an image field.

Abstract: Presented is a system and method for measuring the refractivity profile of a parcel of atmosphere comprising an image capturing device for capturing an image of a visual feature, such as a topographic feature like the horizon, combined with a lens having focal length adapted to focus an image onto image capturing device such that the combination of the lens and the image capturing device are adapted to resolve at least 100 microradians of angle, and an image processor adapted to compare a detected position of the visual feature in the image to the expected position of the visual feature. The system uses the difference between the detected position and the expected position to detect the change in arrival angle caused by atmospheric refraction of light from the visual feature as it passes through the atmosphere.

Abstract: A refractometer has a housing (1), a measurement cell (8) arranged in the housing (1), and a lid unit (2). The lid unit has a base plate (3) with a cutout (7) allowing access to the measurement cell, and a lid (4) for covering the measurement cell. The lid is connected to the base plate by way of a hinge. The lid unit also has a lid insert (11, 17, 18, 28, 31, 35, 39) that is arranged replaceably in the lid. The lid unit (2) is detachably connected to the housing by means of a connecting element that is itself connected to the base plate.